1. Field
The present invention relates to a liquid crystal display element and in particular to a liquid crystal display element of the field sequential system.
2. Description of the Related Art
In recent years, a field sequential liquid crystal display element that does not require a color filter has been developed. In the field sequential system, light sources of three colors RGB are switched at high speed to provide a color display. Thus, the field sequential system does not use a color filter for a typical liquid crystal display element but uses a counter substrate including; a counter electrode containing a transparent conductive film; and a light-shielding film containing a Cr film. The counter electrode is extended to the exterior of a pixel region and electrically connected to an electrode and a wiring provided on the alley substrate.
Since fast response is required in the field sequential liquid crystal display element, a ferroelectric liquid crystal is used as a liquid crystal enclosed between a pair of substrates forming a liquid crystal display element. To enclose a liquid crystal, there has been known a manufacturing method including dropping a liquid crystal on one substrate, applying a sealing material on the periphery of the pair of substrates, laminating the pair of substrates, and curing the sealing material with heat or light to enclose a liquid crystal. In case a ferroelectric liquid crystal is used as a liquid crystal material, a liquid crystal layer between a pair of substrates forming a liquid crystal display element has an optimum thickness range of 1 to 3 μm which is smaller than that of a typical liquid crystal layer. Thus, in some cases, a spacer is arranged to keep uniform the thickness of a liquid crystal layer in a pixel region.
In the process of laminating a pair of substrates, in case the gap between the pair of substrates is small, the sealing material between the pair of substrates spreads and the uncured resin of the sealing material extends to a region where the liquid crystal is enclosed thus contaminating the liquid crystal and degrading the display quality. While this phenomenon does not occur when the viscosity of the sealing material is increased, the sealing material does not sufficiently squash at a time of laminating the pair of substrates; therefore, the gap on the periphery of the panel increases. This results in the difference in the liquid crystal layer between the periphery and center of the pixel region, thus causing uneven display (for example, see JP-A-2003-280007 (FIG. 6)). That is, reduction of the thickness of a liquid crystal layer than a typical thickness may cause the degrading of display quality or uneven display.
There has been a technique for, reducing the thickness of a liquid crystal layer in a pixel region while maintaining good curing of a sealing material. In this technique, a liquid crystal layer thickness adjusting film is provided for adjusting the thickness of a liquid crystal layer in a region surrounded by a sealing material applied to the periphery of a counter substrate and forming thereon a counter electrode (for example, see JP-A-2003-264606 (FIG. 4)).
With the above approach, it is possible to avoid phenomenon concerning curing of a sealing material while reducing the thickness of a liquid crystal layer in a pixel region surrounded by the sealing material, but may cause a crosstalk. Use of this approach makes it necessary to form an insulating film serving as a liquid crystal layer thickness adjusting film between a light-shielding film and a counter electrode on a counter substrate. This is because the counter electrode is used to apply a voltage on a liquid crystal and is preferably provided at the top of layers (the remotest layer from a glass substrate) except an alignment layer, and a light-shielding film is preferably formed on a glass substrate from the viewpoint of adhesion to the base material and optimization of the reflection prevention effect.
While the aforementioned phenomenon is prevented by this structure, horizontal crosstalk may occur. Since the specific resistance of a transparent conductive film used for a counter electrode is about 0.00002 Ωcm and its thickness is a mere 0.1 μm, the resistance of the counter electrode is far from low. Thus, in a portion remote from the joint with an array substrate external to a pixel region, that is, near the center of the pixel region, the resistance component of the counter electrode is added between the pixel region and the array substrate, which may result in defective display called horizontal crosstalk. A transparent conductive film on a typical counter substrate is laminated on a low-resistance metal layer such as a light-shielding film thus suppressing horizontal crosstalk caused by an increase in the resistance component.
With the above approach, the laminating structure of a counter electrode and a light-shielding film in a pixel region is interrupted by the formation of an insulating film in the pixel region as the solution means. Thus, the low-conductive metal film in a light-shielding film does not fully contribute to the conductivity of the counter electrode. As a result, the counter electrode has high resistance thus causing horizontal crosstalk.